This application relates to optical quality polycarbonates having reduced static charge, and to methods of preparing such materials.
Polycarbonates have become the material of choice for the manufacture of optical information storage media such as audio disks, digital video disks, laser disks, optical disk memories and magneto-optical disks to which information may be written and from which it may be read from a laser. For use in these applications, polycarbonates are preferably made by a melt process, such as that disclosed in U.S. Pat. No. 5,606,008, which is incorporated herein by reference. This type of process not only avoids the use of highly toxic phosgene, which is required for manufacture of polycarbonates using the older interfacial (IF) process, it also provides a product with superior optical properties. One of the challenges facing polycarbonates manufactured using a melt process, however, is the control of static charge, since such static charge can itself interfere with read/write functions and attract a film of dust which also reduces the performance of the optical information storage media prepared with the polycarbonate.
Reduction of static charge in polycarbonates has generally been achieved through the introduction of antistatic additives. For example, Japanese Patent No. 62207358 discloses the use of phosphoric acid esters as antistatic agents, while U.S. Pat. No. 5,668,202 discloses the use of sulfonic acid sulfonium salts. Additional additives which can function as antistatic agents are distearylhydroxylamine, triphenylphosphine oxide, pyridine-N-oxide and polyoxyethylene compounds as disclosed in commonly assigned U.S. patent application Ser. Nos. 08/989,552, filed Dec. 12, 1997, and 09/161,563, filed Sep. 28, 1998, which are incorporated herein by reference.
While such additives are effective to a substantial extent, they are not without some drawbacks. Like all additives which are not an integral part of the polymer structure, they are prone to leaching, and may also undergo side reactions or otherwise impair the properties of the polycarbonate product. Thus, there remains room for improvement in the manufacture of optical quality polycarbonates.
It is an object of the present invention to provide optical quality polycarbonates with reduced static charge.
It is a further object of the present invention to provide a method for making such polycarbonates.